(Bug 42803) Apply I/B minimization to incoming HTML

* Minimizes I/B tags on incoming HTML.
* Added a bunch of parsoid-only html2wt tests with expectations
  about this code (all tests pass).

Change-Id: I9dc00f6d05932bdfd8e7586323abe44addfc26ff
Merge "(Bug 42803) Apply I/B minimization to incoming HTML"